When a user account is deleted, the account and email are actually archived. This means two things:
The email address cannot be used as it is still associated with the archived account
The user account can be restored if needed!
To restore a deactivated user account, head to the accounts section and click on the + button as if you were creating a new user account. Fill in the details and, crucially, enter the email address of the user account you want to restore.
A pop up will appear stating that there is an archived user account with that email address, you can either restore or cancel. Click restore and you will be taken to the restored user account where you can make any necessary changes.
Video walkthrough